The present invention relates to a method for milling a planar surface and a milling tool for implementing such a method.
The invention relates more particularly to a method for milling a planar surface, according to which a milling cutter, the rotation axis of which is perpendicular to the surface to be machined, is moved in a direction parallel to the plane of the surface so as to machine the latter in a single machining operation to a predetermined material thickness by means of a single milling head.
A favored, but nonlimiting, application thereof is in the machining of an internal combustion engine casing upper face.
A casing upper face is generally machined with the aid of a milling cutter which is moved horizontally over said upper face. Machining is broken down into a number of operations, including a first rough machining step, during which the material is removed to a first thickness, and one or more finish machining steps, during which the rough-machined surface is successively machined.
Milling cutters called “stepped” milling cutters are known, comprising a rotation axis perpendicular to the surface to be machined, an upper row of edges distributed around a first circumference and a second, lower row of cutting edges distributed around a second circumference which is axially offset with respect to the first circumference. The two rows of edges are coaxial and offset both axially and radially. The milling cutter carries out the rough machining step and the finish machining step by machining the surface of the casing at two different heights during a single machining operation.
In another type of milling cutter, called a “spiral milling cutter”, the edges are arranged in a spiral shape around the body of the milling cutter, with an axial and radial offset between each edge. During machining, each cutting edge machines a portion of the part at a different axial height. The overall depth of pass of the tool is thus distributed between the different edges of the tool. This arrangement makes it possible to increase the thickness removed in a single tool passage. However, it reduces the service life of the tool and there is a significant risk of scratches on the machined surface.